1. Technical Field
The present invention relates to an image processing apparatus, an image processing method, an image processing program, and an image processing system, and relates to the image processing apparatus, the image processing method, the image processing program, and the image processing system suitable for being used in a copy machine or a multi function peripheral (MFP) having this function.
2. Background Art
In recent years, a digital color copy machine with high image quality capable of copying an image faithful to an original image has been put into practical use. Therefore, there is a risk of forgery of paper currencies or securities by copying them with high image quality.
As a countermeasure against such a forgery, a symbol image pattern of the paper currencies or securities, etc, is previously stored in the copy machine, and when image data read from the paper currencies or securities set on a manuscript platen is identical to its stored symbol image pattern, a function of stopping a copying operation or preventing a normal copying operation is considered.
However, a large storage capacity is required for storing symbol image data of all paper currencies or securities, thereby prolonging a processing time, and an execution is likely to be difficult. Further, if new paper currencies or securities appear, illegal copying can not be prevented, thus making it difficult to cope with such a situation by a conventional technique.
Therefore, there is provided a technique in which information for specifying a manufacturer's model name of a machine used in copying, serial numbers, and time and date of making a copy, is turned into a tracing pattern, and this pattern is printed on a copy itself with an ink hardly visible to human eyes normally. The machine used in a copying object can be specified later, and therefore such a technique is indirectly useful for preventing the forgery of the paper currencies or securities.
For example, as shown in FIG. 5, this is a technique in which a tracing pattern 5 consisting of small (such as 1 pixel) dots is disposed in symbol image data 3 of a paper currency 1, and image data 3 including this tracing pattern 5 is printed on a copying paper.
Note that in order to suppress to minimum a deterioration of an output image due to addition, the tracing pattern 5 is generally printed by using a yellow color material.
Japanese Patent Laid Open Publication No. 2003-234886 (Patent document 1) is given as such a technique.
According to this patent document 1, a forming area of a tracing dot pattern is divided in accordance with the contents of the tracing information, dots of a large size are added to an area indicating the most important start mark or maker ID, dots of a medium size are added to an area indicating individual ID such as a serial number important next and dots of a small size are added to the other information area. Consequently a trace pattern is added so that more important information can be easily detected while suppressing the deterioration of picture quality, and a forgery prevention effect is improved.
Further, Japanese Patent Laid Open Publication No. 06-62217 (Patent document 2) is also proposed.
According to the patent document 2, a modulating unit modulates a symbol pattern outputted from a symbol pattern generating unit corresponding to the intensity of an image signal, and this modulated symbol pattern and the image signal are synthesized by a synthesizing unit. By modulating the added symbol pattern corresponding to the intensity of the image signal, the symbol pattern is added so as not to be hidden in the image signal in the copied image, thus preventing the forgery of the paper currencies, etc.
However, in the aforementioned patent document 1 and the patent document 2, the tracing pattern is added at a determined position in each image data or the image signal. Therefore, even if the addition of a pattern is performed in a hardly visible form, it can be easily judged that some sort of information is added to the image, if the image processed by printing or the like is analyzed.
Therefore, there is a problem that alteration is performed in anticipation of such a case, so that the image data such as masking an added position of the tracing pattern is previously prepared and the tracing pattern is made hardly recognized.